Loops in R forward and back

Printing Series Using Loops in R

In this tutorial, we will learn how to print different numerical series using loops in R, including their reverse versions. We will use for, while, and repeat loops.

1. Series: 1, 2, 3, ..., 10

Using for loop

for (i in 1:10) {
  cat(i, ",")
}

Using while loop

i <- 1
while (i <= 10) {
  cat(i, ",")
  i <- i + 1
}

Using repeat loop

i <- 1
repeat {
  cat(i, ",")
  i <- i + 1
  if (i > 10) break
}

Reverse:
for (i in 10:1) { cat(i, ",") }

2. Series: 2, 4, 6, 8, 10

for (i in seq(2, 10, by=2)) {
  cat(i, ",")
}

Reverse:
for (i in seq(10, 2, by=-2)) { cat(i, ",") }

3. Series: 1, 3, 5, 7, 9

for (i in seq(1, 10, by=2)) {
  cat(i, ",")
}

for (i in seq(9, 1, by=-2)) { cat(i, ",") }

4. Perfect Squares: 1², 2², ..., 10²

for (i in 1:10) {
  cat(i^2, ",")
}

for (i in 10:1) { cat(i^2, ",") }

5. Special Series: n(n+1)

Output: 2, 6, 12, 20, 30, 42, 56, 72, 90

for (n in 1:9) {
  cat(n * (n + 1), ",")
}

for (n in 9:1) { cat(n * (n + 1), ",") }

6. Alternating: 1, -1, 1, -1, ...

for (i in 1:10) {
  cat((-1)^(i + 1), ",")
}

vec <- c()
for (i in 1:10) vec[i] <- (-1)^(i+1)
cat(rev(vec), sep = ",")

7. Alternating Signed Numbers: 1, -2, 3, -4, ...

for (i in 1:10) {
  cat(i * (-1)^(i + 1), ",")
}

vec <- c()
for (i in 1:10) vec[i] <- i * (-1)^(i+1)
cat(rev(vec), sep = ",")

🧠 Summary

Series	Logic	Loop Type
1 to 10	1:10	for, while, repeat
Even	i %% 2 == 0	for
Odd	i %% 2 == 1	for
Squares	i^2	for
n(n+1)	n*(n+1)	for
1, -1, 1, ...	(-1)^(i+1)	for
1, -2, 3, ...	i * (-1)^(i+1)	for

💡 Tip: Use cat() for inline printing, rev() for reverse, and seq() for stepwise sequences.